1. Field of the Invention
The present invention relates to an imaging apparatus using a solid state imaging element and particularly to an improvement in the mechanism for enhancing resolution by shifting the imaging position of the light from the subject which enters the solid state imaging element, in a pixel arrangement direction in a light receiving plane nearly vertical to the axis of the incident light.
2. Description of the Related Art
Generally, the solid state imaging element such as a charge coupled device has a plurality of pixels arranged so as to form a two-dimensional matrix, and the resolution of an image is substantially determined by the number or pixels in the light receiving plane. Accordingly, all that is needed to achieve higher resolutions is to increase the number of pixels of the solid state imagine element, but from aspects of present techniques and costs the increase in number of pixels has its limit.
FIG. 25 illustrates the principle of the prior art disclosed in Japanese Unexamined Patent Publication JPA 60-54576 (1985) and Japanese Unexamined Patent Publication JPA 61-251380 (1986). A flat refracting plate 100a is interposed in the middle of the optical axis 100 of the light incident from a subject to a light receiving plane. When the refracting plate 100a is inclined by an angle .theta. from the state shown by a two-dot chain line vertical to the optical axis 100, the incident light 101 is displaced from the optical axis 100 by a shift .DELTA. which is obtained by the following formula (1): ##EQU1## wherein "t" and "n" are the thickness of the refracting plate, and the index of refraction of the glass which is a material of the refracting plate, respectively.
If the inclination angle .theta. of the refracting plate 100a is changed, it is possible to shift the imaging position of the incident light 101 from the subject in relation to the light receiving surface of the solid state imaging element in the horizontal and perpendicular directions of the pixel arrangement by an infinitesimal distance less than the pixel arrangement pitch. When a plurality of images obtained by shifting the incident light 101 are comprised on an image memory, then the number of the pixels of the solid state imaging element apparently increases, and images with higher resolutions can be obtained.
FIGS. 26, 27 are views showing the constitution of the prior art disclosed in Japanese Unexamined Patent Publication JPA 61-251380 (1987), that is, a sectional side view and a front view, respectively. The transparent flat refracting plate 100a made of a material such as glass is disposed between a lens 100b and a solid state imaging element 100c so as to traverse the optical axis 100 of the lens 100b. The refracting plate 100a is rectangular, in the center of each side of which is mounted a supporting member 100d having a L-shaped section, and a coil 100e is fixed on the longer side of each supporting member. A movement limiter 100f is provided on the shorter side of each supporting member so as to hold each supporting member 100d. A magnet 100m and a yoke 100y are arranged in the vicinity of each coil 100e. The movement limit 100f, magnet 100m and yoke 100y are fixed on the cabinet side of the imaging apparatus main body. An electromagnetic driving force is generated to the magnetic flux of the magnetic circuit which is formed between the magnet 100m and the yoke 100y, by the current in the coil 100e, acting as driving force to advance and retreat each coil 100e in a direction along the optical axis 100.
Now, it is assumed that one pair of adjacent coils 100e containing a corner are driven rightward along the optical axis and the other pair of coils 100e containing a corner are driven leftward along the optical axis. One of two corners confronting each other of the refracting plate 100a advances along the optical axis 100 and the other of the two corners retreats along the optical axis 100. The shorter sides of the supporting member 100d mounted on each side of the refracting plate 100a are respectively contacted to the move limiter 100f, and, as a result, the refracting plate 100a inclines to the optical axis 100 by a certain angle. In Japanese Unexamined Patent Publication JPA 60-54576 (1985), a piezoelectric element is used as an actuator instead of an electromagnetic actuator disclosed in Japanese Unexamined Patent Publication JPA 60-251380 (1985), and their fundamental constitutions are the same.
FIG. 28 is a view showing the constitution of a gimbaling mechanism as disclosed in Japanese Unexamined Patent Publication JPA 4-211217 (1992). In this prior art, two dimensional optical scanning is conducted using a gimbaling mechanism element. A first oscillator 200 includes a frame 201 which comprises a pair of rotation supporting portions 202, 203, in the center of which a reflection mirror 204 is installed. A second oscillator 205 includes a frame 206, and a pair of rotation supporting portions 207, 208, in the center of which the first oscillator 200 is installed. The rotation axis of the rotation supporting portions 202, 203 is at right angles to the rotation axis of the rotation supporting portions 207, 208. The first and second oscillators 200, 205 are independently rotated and oscillated about respective rotation axes by electrostatic force. When the reflection mirror 204 is exposed to the incident light from a subject in a state that the first and second oscillators 200, 205 are rotated and oscillated about the two orthogonal axes, the angle of the reflected light is altered and, as a result, the optical path can be changed. By applying this constitution, the resolution of the solid state imaging element can be enhanced like the case as shown in FIG. 25 where refraction of light is taken advantage of.
FIG. 29 is a view showing a simplified electrical constitution for screen composition aiming at enhancing the resolution. Memories 301-304 which have a storage capacity corresponding to the number of the pixels of the solid state imaging element are provided, and input signals representing an image formed by shifting the imaging position each period of four division frame periods T1-T4 are changed over to store the image data in the respective memories 301-301. When the image data from the respective memories 301-304 are composed in a memory 305, an image for one frame whose resolutions in the length and width directions are doubled can be obtained as a whole.
In the prior art as shown in FIGS. 26, 27, since the inclination angle .theta. of the refracting plate 100a depends on the traveling distance of the supporting member 100d until the shorter side of the supporting member 100d contacts with the movement limiter 100f, the inclination angle .theta. is determined by only one variable and thus it is difficult to select the desired resolution. In addition, there are some cases where the refracting plate 100a is required to be inclined a plurality of times within a short period, in which cases, if driven at high speeds, repeated contact between the movement limiter 100f and supporting member 100d may cause their wear, thus resulting in lowered precision of the inclination angle .theta. and further impairment of their durability. In addition, the noise which occurs at the time of contact grows to levels which are no longer negligible the driving speed increases.
Furthermore, in the prior art as shown in FIG. 28, the use of the two uniaxial oscillator results in an increased parts count, a complicated configuration and consequently poor assembling efficiency. Moreover, since the first oscillator 200 is secured to the second oscillator 205, the weight of the second oscillator increases, thus resulting in greater driving force due to the increased inertia moment.
As still another constitution mat be feasible such a constitution that the refracting plate is inclined by the couple of forces generated by a pair of voice coil motors facing across the axis of rotation. In such constitution, the difference in thrust between the pair of voice coil motors causes oscillation in the vertical direction to the refracting plate. When the oscillation gain is increased, the oscillation acts as disturbance to the circumference of the rotation axis in a control direction and the servo controllable range is thus limited.